PROJECT SUMMARY Active engagement in HIV care is critical to optimize treatment outcomes among individuals living with HIV. This is especially true for men who have sex with men (MSM), a group disproportionately affected by HIV and continuing to experience high incidence rates. Social support, particularly in the context of primary romantic relationships, has consistently been documented as a predictor of health behaviors, including adherence to care for HIV and other conditions. As such, couples-based interventions have the potential to create a lasting effect on engagement in HIV care, uptake and adherence to pre-exposure prophylaxis (PrEP) for HIV prevention, and other health behaviors among MSM in primary relationships with other men. Building on years of formative work documenting couple-level effects on engagement in care among HIV serodiscordant and seroconcordant positive male couples, we have developed and piloted a couple-level intervention grounded in Social Control Theory aimed at improving engagement in care and virologic outcomes. We now propose to evaluate this intervention in a randomized controlled trial comparing virologic outcomes of couples randomized to the couple-level intervention or to an individual intervention. If the couple-level intervention proves efficacious, it will provide a potentially cost-effective and sustainable approach to optimizing treatment outcomes and reducing risk of new HIV transmissions among this population. This may, by extension, be subsequently adapted for other couples, other settings (including PrEP), and other health conditions that demand active patient engagement such as diabetes, cancer, and heart disease.